Menu for a Japanese inspired summer dinner party?

Bowls of edamame (Trader Joe's frozen are great)

These okonomiyaki are delicious and would disappear in a minute. But they require frying. Maybe you have, or can borrow, an electric skillet? You could plug it in outside, on a heavy-duty utility extension cord (don't use a regular extension cord), and enlist someone to help fry the batches. They don't take long at all.
https://food52.com/recipes/12352-okonomiyaki

and here's my ASCII art for Chicken Yakatori. Cut your chicken in strips, cut your green onions to size of the strips. Line up the chicken strips and green onions like this: [|[|[|[|[|
Alternating chicken and green onion. Then work in TWO skewers like this:
=[|[|[|[|[|[= this makes them easy to turn on the grill and really holds the green onion flavor to chicken.
If you do shrimp you do this: =))))))=

You can make both those the night before ready for the grill the next day.
Get some Ponzu sauce and add a bit of ginger juice and lime juice for a dipping sauce for shrimp.

Gomae. Chilled spinach with a seasame dressing. (Shhh Just get a bottle of the Kewpie brand). Use a sushi matte to make press the spinach into rolls. And slice them up dress them and decorate with sesame seeds.
Another good summer dish is Sunomono Salad: A vinagards salad with cucumber, wakame seaweed (fresh stuff if you can get it) and crab or octopus. You can make this overnight or a couple of hours before.

I love chawanmushi. It is a very refreshing dish -- you can make it ahead and keep in the fridge. Chef Anita Lo has a corn version in her book "Cooking without borders"

How about homemade mochi for dessert? Two Red Bowls posted a recipe here on this site. If you look down at the comments, you will see a link to her blog where people had all kinds of flavor ideas. I know it's not the real thing, but I love the mochi at Trader Joe's. Making your own sounds easy and fun.

How about japanse street food? Or as mentioned, cold soba. Not to mention rice balls are very good as a great appetizer. I am having something similar and everyone is bringing their favorite asian dish. Hope all goes well.

Chicken yakitori skewers will be perfect for the barbecue. Serve those along with chirazhi sushi - basically, deconstructed sushi - an excellent way to make and serve sushi for a crowd. If you and your guests are up for it, cold soba noodles are great for summer too, but it's an acquired taste. For dessert - perhaps buy some mochi, or pancakes filled with red bean filling, and serve with green tea ice cream.